The present invention relates to a fuel pump for use with an automobile, for example, and more particularly to a fuel pump which may reduce a noise generating therefrom.
FIGS. 11 to 18 show a fuel pump in the prior art. Referring to FIG. 11, reference numeral 2 designates a fuel pump substantially vertically mounted in a fuel tank 4 through a bracket 6.
Referring to FIG. 12, the fuel pump 2 is generally constructed of a cylindrical housing 8, a motor section 10 mounted in the housing 8 at its substantially upper portion, and a pump section 14 fixedly mounted below the motor section 10 with a cover member 12 interposed therebetween.
A motor shaft 18 for a rotor 16 of an electric motor constituting the motor section 10 is inserted through a central hole of the cover member 12 with a bearing 17 mounted therein. The motor shaft 18 extends into the pump section 14, and first and second impellers 20 and 22 are mounted on the motor shaft 18 so that they may be rotated with the motor shaft 18 but they are slidable in the axial direction of the motor shaft 18. As shown in FIGS. 13 and 14, each of the first and second impellers 20 and 22 is formed at its outer circumference with a plurality of recesses 24 to form a plurality of vanes 25. The vanes 25 are formed in upper and lower lines in such a manner that the upper vanes 25a are arranged alternately with respect to the lower vanes 25b. Referring back to FIG. 12, a housing body 26 is fixed by means of screws 32 to the cover member 12 through a pair of annular spacers 30 and 31 and an intermediate plate 28 fixed between the annular spacers 30 and 31. There are defined first and second annular gaps between the inner circumference of the lower spacer 30 and the outer circumference of the first impeller 20 and between the inner circumference of the upper spacer 31 and the outer circumference of the second impeller 22. The housing body 26 is formed on its upper surface with a first fuel groove 40, and the intermediate plate 28 is formed on its lower surface with a second fuel groove 38, thus defining a first pump chamber 42 having a C-shaped cross section around the outer circumference of the first impeller 20 by the first annular gap, the first fuel groove 40 and the second fuel groove 38. Similarly, the intermediate plate 28 is formed on its upper surface with a third fuel groove 36, and the cover member 12 is formed on its lower surface with a fourth fuel groove 34, thus defining a second pump chamber 44 having a C-shaped cross section around the outer circumference of the second impeller 22 by the second annular gap, the third fuel groove 36 and the fourth fuel groove 34. The first pump chamber 42 and the second pump chamber 44 are communicated with each other through a communication hole formed through the intermediate plate 28. The first pump chamber 42 is communicated at its upstream end with an inlet port 48 formed through the housing body 26 which inlet port 48 is communicated into the fuel tank 4, while the second pump chamber 44 is communicated at its downstream end with an outlet port 46 formed through the cover member 12 which outlet port 46 is communicated into the housing 8. Although not seen, there are defined small clearances between the upper surface of the housing body 26 and the lower surface of the first impeller 20 and between the upper surface of the first impeller 20 and the lower surface of the intermediate plate 28. Similarly, there are also defined small clearances between the upper surface of the intermediate plate 28 and the lower surface of the second impeller 22 and between the upper surface of the second impeller 22 and the lower surface of the cover member 12. Further, the cover member 12 and the housing body 26 are formed at the respective central portions with recesses 33 and 35, respectively, and the intermediate plate 28 is formed at its central portion with a through-hole 37. Each of the first and second impellers 20 and 22 is formed with four communication holes 39 for communicating the recesses 33 and 35 and the through-hole 37 with each other, thereby defining a pressure balancing chamber for maintaining the pressure constant at the small clearances mentioned above. Accordingly, the first and second impellers 20 and 22 can be smoothly rotated under the balanced fuel pressure.
In operation, when the first and second impellers 20 and 22 are rotated, the fuel pressure in the first pump chamber 42 is increased to feed the fuel into the second pump chamber 44 through the communication hole of the intermediate plate 28. The fuel pressure in the second pump chamber 44 is further increased to feed the fuel through the outlet port 46 into the housing 8. Thus, the fuel pressure in the pump chambers 42 and 44 is increased by the two-stage pressure increasing operation of the first and second impellers 20 and 22, so that the fuel is sucked from the inlet port 48 and is fed under pressure through the pump chambers 42 and 44 into the housing 8.
Referring to FIG. 13 which is a cross section taken along the line F--F in FIG. 12, the fuel groove 40 is formed in a C-shaped configuration on the upper surface of the housing body 26 along the inner circumference of the annular spacer 30. A portion of the inner circumference of the annular spacer 30 corresponding to a portion of the housing body 26 where the fuel groove 40 is not formed is radially inwardly projected to form a partition wall 50. An inner circumferential edge 52 of the partition wall 50 is formed arcuately in such a manner that a curvature of the inner circumferential edge 52 is substantially equal to a curvature of the outer circumferential edge of the first impeller 20. With this construction, there is no gap between the outer circumferential edge of the first impeller 20 and the inner circumferential edge 52 of the partition wall 50 of the spacer 30. Accordingly, the first pump chamber 42 is limited at its opposite ends by the partition wall 50. That is, the fuel sucked from the inlet port 48 and increased in pressure is struck against the side surface of the partition wall 50, and is then fed to the communication hole communicated with the second pump chamber 44.
Referring to FIGS. 15 and 16 which show a modification of the construction shown in FIGS. 13 and 14, the downstream end portions of the fuel grooves 38 and 40 are diverted outwardly in the radial direction of the housing body 26. This construction is described in detail in Japanese Patent Application No. 62-335239 filed by the present assignee (which corresponds to Japanese Patent Laid-open Publication No. 1-177491). Similar to the construction shown in FIGS. 13 and 14, the first pump chamber 42 is limited at its opposite ends by the partition wall 50. The fuel sucked from the inlet port 48 and increased in pressure is struck against the side surface of the partition wall 50, and is then fed to the communication hole.
Referring to FIGS. 17 and 18 which show another modification of the construction shown in FIGS. 13 and 14, the downstream end portions of the fuel grooves 38 and 40 are curved toward the center of the housing body 26. This construction is described in Japanese Patent Application No. 62-335237 filed by the present assignee (which corresponds to Japanese Patent Laid-open Publication No. 1-177489). The first impeller 20 is formed at its central portion with a plurality of windows 56 which are adapted to be communicated with the communication hole of the intermediate plate 28. Thus, the fuel increased in pressure in the first pump chamber 42 is fed through the windows 56 to the communication hole.
In the fuel pump 2 as mentioned above, there is generated a high-frequency noise (so-called impeller noise) having a high frequency to be represented by (the number of the vanes of the impeller).times.(a rotating speed per second of the impeller). It is considered that the generation of such an impeller noise is caused by the following reasons. That is, since edges 154, 154a and 154b of the fuel grooves 38 and 40 angularly intersect the vanes 25 as shown in FIGS. 14, 16 and 18, the fuel in the fuel grooves 38 and 40 is suddenly sheared when the vanes 25 cross the intersecting edges 154, 154a and 154b of the fuel grooves 38 and 40. FIG. 19 shows an accoustic pressure measured at a point M (see FIG. 11) away by about 10 cm from the outer surface of the fuel tank in case of using the fuel pump as shown in FIG. 15 under the condition of (the number of the vanes).times.(the rotating speed of the impeller)=3000/sec. As apparent from FIG. 19, the impeller noise appears at the frequency of 3 kHz.
Recently, the silentness in the compartment has been improved to result in a relatively large percentage of the impeller noise accoustically perceived in the compartment. Accordingly, it is required to reduce the impeller noise. As the fuel pump is normally located behind a rear seat as shown in FIG. 11, such requirement is increased particularly in a high-grade car which requires the silentness especially at the rear seat.